DOEYDEEilA. 49 



DoRTDERMA RcEMERi, //m<Z^. (Plate VIII. figs. 3, 3 «, 3 i.) 



1808. A ramose Alcyonite, Parkinson, Org. Rem. vol. ii. p. 92, t. 7. f. 7, 12. 

 1864. Polyjerea dichotoma, F. A. Roem. Palaeont. Bd. 13, p. 36, t. 14. f. 1. 

 1878. Polyjerea dichotoma, Qiienst. Petref. Bd. 5, p. 423, t. 135. f. 10, 11. 

 1878. Doryderma dichotoma, Zitt. Studien, II Ab. p. G7, t. 7. f. 1. 



Sponge branching, consisting of a thick stem from which short branches are given 

 off in an irregular manner. The stem and branches traversed by numerous vertical 

 canals about 2 mm. each in diameter. The interspaces of the mesh at the surface 

 are from 1 mm. to 1-25 mm. in width. The spicules are -1575 mm. in thickness, 

 and occasionally 2 mm. in length. A dermal layer is formed by numerous trifid 

 spicules, whose shafts fill the interspaces of the mesh, whilst their trifid summits 

 slightly project outwards. 



F. A. Rcemer's specific name, dichotoma, having been previously employed by 

 Miss Benett for a sponge of this genus, it is necessary to give another designation 

 to his species ; and I have therefore termed it Rcemeri, in memory of its discoverer. 

 From an examination of undoubted examples of this species, from the Upper Chalk 

 of Brunswick, presented to the Museum by Prof. Zittel, I am enabled to determine 

 its distinctness from either of the two foregoing species. It is mucli less regular in 

 its habit of growth, the stem is much thicker, and the mesh interspaces are notably 

 larger than in D. ramosum and B. dichotomum, Benett. The specimens appear to be 

 rare in the Chalk of this country, and are only met with in the interior of flints. It 

 is very seldom that the dermal trifid spicules are preserved ; but I have detected them 

 in one or two fragments in the Collection. 



Distribution. Upper Chalk : Wiltshire ; Brunswick [Zitt. coll.). 



Doryderma Benetti, Hinde, n. sp. (Plate IX. figs. 1, 1 «, 1 h.) 



1808. An Alcyonite, Parkinson, Org. Rem. vol. ii. t. 10. f. 6. 



1831. Polypothecia, Benett, Cat. Org. Rem. Wilts, t. 10. f. 1. 



1847. Non Jerea elongata, Mich. Icon. Zoophy. p. 134, t. 29. f. 4. • 



1854. Jerea Carteri, p. p., Morris, Cat. Brit. Foss. p. 28. 



Sponges simple, massive, elongate pear-shaped, or with a cylindrical body sup- 

 ported on a relatively thin stem, occasionally also subglobate. The summit is 

 either rounded, horizontally truncate, or obtusely conical. In some examples the 

 body gradually tapers downwards to the stem, in others there is a distinct constriction 

 between the basal portion of the body and the top of the stem. There is great 

 variability in the size of different examples — the smaller forms measure 72 mm by 

 42 mm., whilst the larger specimens reach a length of 390 mm. and a width of 

 125 mm. 



The body of the sponge is penetrated by numerous straight vertical canals, 2 5 mm. 

 each in width, which open at the summit in close proximity to each other. A few 



H 



